Electricity charges collected by electric power companies from users are generally divided into two categories, the energy charge and the demand charge. The energy charge is the charge of the total electricity consumed by the user during a certain period of time (e.g., during a billing month), wherein the unit of the energy is charged by kWh (kilowatt-hour). With respect to the energy charge, the electric power companies usually implement time-dependent electricity prices (i.e. setting different electricity price rates for different periods) and, thereby, guiding the users to reduce the electricity consumption during the peak period. As to the demand charge, it is the charge collected by the electric power company according to a maximum demand of the user during a certain period of time (e.g., during a billing month), wherein the unit of the demand is charged by kW. Different electric company calculates “demand” in different ways and, generally, the demand is calculated according to the average electricity consumption power during a certain period of time (e.g., 15 minutes, or longer or shorter than 15 minutes). The electric power company collects a fixed demand charge according to a contracted capacity signed with the user in advance. The electric power company will collect an additional charge if the maximum demand of the real power consumption of the user exceeds the contracted capacity. By setting the contracted capacity and collecting the demand charge, the electric power company can more easily control the peak load of the overall electric power system.
To reduce the energy charge and the demand charge, many users utilize storage batteries in order to reduce the peak electricity consumption of the power supply system of the electric power company, maintain a stable electricity consumption power, and reduce the maximum demand. Generally speaking, the user may charge the storage batteries during the off-peak electricity price period where the electricity price rate is relatively low (or during the off-peak power consumption period where the power consumption is relatively low) and discharge the storage batteries during the peak electricity price period where the electricity price rate is relatively high (or during the peak power consumption period where the power consumption is relatively high). By controlling the charge and discharge of the storage battery, load shifting and peak load shaving can be achieved and, thereby, reducing the energy charge and the demand charge.
Currently, technologies that use storage batteries for peak load shaving can be classified into three categories. Technologies of the first category charge and discharge the storage batteries at fixed times without considering the variation of the real load of the users. Technologies of the second category discharge the storage batteries when the real load of the user is greater than a threshold or discharge the storage batteries when the electricity price rate exceeds a threshold. Technologies of the third category predict a load curve in advance and then decide the charge and discharge of the storage battery according to the predicted load curve. Technologies of the aforesaid first and second categories do not consider the time at which the maximum load actually occurs, while technologies of the third category cannot deal with the situation that the real load is different from the predicted load. Therefore, the conventional technologies for peak load shaving by using the storage battery still need to be improved.
Accordingly, there is still an urgent need for a charge and discharge control technology which can shave the peak load by the storage battery efficiently and, thereby, reducing the demand charge and the energy charge of the user and reducing the overall peak load of the power supply system of the electric power company.